Electronically-operated music instrument



April 16, 1957 R. sEYBoLD ELEcTRoNmALLy-OPERATED Musrc INSTRUMENT FiledMarch 12, 1952 'KAB Il Ir ui K K4 K3K K1 IVNvsNTIoR.

xpa-

Nei;

l"GL

United States Patent Office ELECTRONICALLY-OPERATED MUSIC INSTRUMENT RenSeybold, Strasbourg, France Application March 12, 1952, Serial No.276,122 Claims priority, application Germany March 16, 1951 Claims. (Cl.841.26)

The present invention relates to electronically operated musicinstruments.

lt is one object of the present invention to provide improvements inelectronically operated music instruments of the type wherein theelectric oscillations corresponding to the different notes aretransmitted through amplifiers to a sound reproducer such as a. loudspeaker.

It is a further object of the present invention to remove thedifficulties encountered in the tuning of instruments of this type andalso to cut out the parasitical noises arising at the beginning and atthe end of each note. Such creaking noises are cut out in accordancewith the present invention by means of a heXode-triode inserted in thecircuit so as to flatten the steep front and rear edges of the waves; tothis end, the grid bias applied to the hexode-triode when inoperative issuch that it blocks completely the entrance of the oscillations into thetubes; the arrival of a pulse shifts then gradually the grid bias tooperative value so as to gradually release correspondingly thekoriginally blocked tube and consequently, after a delay of apredetermined duration, the current may flow at full intensity.Similarly, at the end of the pulse, the opposite phenomenon appearsinasmuch as the grid bias is shifted back gradually from its operativevalue to its blocking value. By reason of this smooth switching in andout of the pulses, the unpleasant creaking noises appearing in the knownarrangements of this type at the beginning and at the end of each notedisappear completely in the present, improved instrument. It is ofadvantage to provide for the blocking of the tube through theapplication of a high negative grid bias so that the pulse correspondingto each note may reduce said bias gradually to a small negative value.

Such arrangements of Vacuum tubes, the conductivity of which variesthrough a modification in the grid bias between a range of blockingvalues and an operative value and reversely, are well known per se andhave been used for various purposes, chiefly for cutting out the echoesin long distance transmissions and in fact certain details developedpreviously in such technical fields may also be resorted to in the caseof the present, improved instrument. It is also possible through amodification of the voltage of the cathode of a variable-mu tubeinserted between the frequency generator and the amplifier as providedby a system of resistances and condensers to release the tube operatingas an amplifier with a suitable delay. It is also known that it ispossible to produce a lasting note by a corresponding frequencygenerator through depression of a key and to transmit it in a mannersuch that the depression and release of said key produces, through amodification in the negative voltage of the control grid of avariable-mu tube, a gradual increase and decrease of the second volume.

lt is still another object of the present invention to provide anelectronically operated music instrument in which the depression of thekey allows the production of the desired note only after a predeterminedperiod of gradual development while the release of the key pro-2,788,693 Patented Apr. 16, 1957 vides for the gradual dying out of thesound which is being no longer produced.

It is of particular interest, for the application to be considered, toresort to a network of condensers and ohmic resistances that isconnected with the grid biasing means. To this end, the condenser isloaded when inoperative through the source of negative potential whichmay be of say -20 volts. When a pulse at the note frequency is fed intothe circuit, the key or the like means produces simultaneously aswitching of the condenser and resistance network in a manner such thatthe condenser discharges across a resistance while on the other hand,the current produced by the source of biasing potential is submitted, onits way, to such a drop in potential that the bias of the grid assumesthe value required for operation of the tube. The time required forshifting the grid potential from its blocking value to its operativevalue is thus equal to the delay required for discharging the condenseracross the resistance. A suitable selection of the value of theseelements allows thus adjusting, within a large range and as desired, thetime of this modification in grid bias and consequently the duration ofthe development of the sound. Thus it is possible to adjust the durationof this development as desired within a range between one thousandth ofa second and several seconds.

The same procedure is obtained in the opposite direction at the end ofthe impulse inasmuch as the discharge circuit of the condenser is brokenand the source of grid bias loads again the condenser gradually andconsequently the bias of the grid assumes gradually a value blocking thetube.

The possibility of adjusting according to circumstances the duration ofthe development and of the dying out of each note allows adapting thesedurations to the requirements of the music. Thus it is possible forinstance to make this duration substantially longer for low notes thanfor high notes, in which latter case the periods considered may becomparatively short and yet cut out the parasitical noises at thebeginning and end of each note. Consequently, the switching means forthe condenser and resistance network should be preferably coupledmechanically with the note producing key, in a manner such that, in thecase of high notes, low capacity and resistance values are insertedwhile large capacity and resistance values are inserted for lower notes.Thus the duration of the development and dying out of a note is definedautomatically in accordance with the note that is being produced throughthe mere depression of the corresponding key.

ln many known electric music instruments, there are provided octaveswitching means that allow upon actuation of a predetermined key toproduce, instead of the note corresponding normally to said key, a notethat is higher or lower than the latter by one or more octaves. Suchoctave switches are coupled with the condenser and resistance networkreferred to hereinabove in a manner such as to provide the execution ofthese conditions. It is of advantage to couple also these switchingmeans controlling the condensers and the resistances with the registersthat define timbre of the instrument.

With these and other objects in view which will hecome apparent in thefollowing detailed description, the

present invention will be clearly understood in connection with ytheaccompanying drawing, in which:

The figure is a diagrammatic showing of the invention. Referring now tothe drawing, the present arrangement includes two main sections. Thesection A forms the frequency generator provided in the case illustratedwith a simple coupling. The section B forms the preliminary amplifierthat serves also for the control of the above-disclosed gradualdevelopment and dying out of the notes. These two sections are coupledthrough the condenser KAB.

The frequency generator A includes two triodes Tl and T2 that are drawnas incorporated into a common tube. The note provided through thisarrangement is defined by the magnitude of the operative portion'of theresistance R2jR3-l-R4Jl-R5'l-R6, the values of these well-definedelementary resistances being such that they produce the notes of thechromatic scale. The insertion of these resistances is provided throughswitches of which only live are illustrated for sake of simplicity byway of exemplifications, to wit the switches K1 to K5. These switchestirst ground the corresponding tapping points on the resistance systemand consequently the wire L which operates as deblockingof thevpreliminary amplitier section B.

The anode of the triode .T1 is connected directly with the grid of thetriode'TZ, :this connection between said anode and said grid beingfurthermore connected through a resistance R01 with a potentiometer P ofwhich one terminal is fed by the supply of energy A2 feeding the anodeof T2, said supply being stabilized by a neon tube NA while the otherpotentiometer end is grounded. The anode resistance R03 of the triode T2is adjustable. The resistance R61 inserted between the anode of T1 andthe potentiometerlJ is designed in such manner that the drop inpotential across it may produce the desired bias for the grid of thetriode T2. A shifting of the rider providing for the tapping on thepotentiometer P produces a modification in the biasing voltage whichleads in its turn to an adjustment of the slope of the characteristiccurves in the triodes T1 and T2 inasmuch as an increase in the slope ofthe triode T2 produces a reduction in the slope of the triode T1 andvice versa. The grid of the triode T1 is grounded through an adjustablecondenser C02.

The condenser K that connects the anode of the triode T2 with thecontrol grid ofthe triode T1 is designed so that the concert pitch besuch that the A of the scale may vibrate at a frequency of 880 cycles.

ln the 'instrument when complete land wherein consequently the magnitudeof the 'different resistances and condenser-s are well-defined, theadjustment to the characteristics of the dierent tubes, which alwaysvary somewhat for tubes of the same type, may be provided with a View toobtaining accurate tuning. This Vtuning may be achieved in threediierent ways. Supposing that the resistances7 which define the pitch,produce a range of 'notes extending over three oc'taves between C1 andC4, it is possible through action on the potentiometer l and on theadjustable resistances 'R02 andRtiS to obtain an accurate tuning for abasic note A1 to l870 or 880 cycles. ln order to allow playing withother instruments and to makeup consequently for' possible differencesin pitch, the adjustable resistance R62 which connects the cathode ofthe triode T1 with'ground is provided. The player may, through asuitablerotary adjustment Vof the resistance R92 raise or lower thewhole pitchofthe instrument so as to prevent any interference whenplaying with other instruments. Furthermore if the magnitudes of thecondensers K and CO2 are adjusted for a predetermined type of vacuumtubes, it isrpossible to provide for a transposition of the scale by oneor more octaves by -increasing or reducing the frequency twice, fourtimes and the like.

The frequency generator A is coupled with the preliminary amplilier Bthrough the above-mentioned coupling condenser KAB and it is thuspossible to 'feed the first control grid 1 of the hexode H through thecurrent at audio frequency produced by the frequency generator A. Thishexode is illustrated inthe drawing as combined in a single Vacuum tubewith a triode T3, although this is not essential.

The wire L fed through the switches K1 to K5 feeds two resistances R4and R2 in series and therethrough it is connected with a supply Gbiasing the grids of the combined hexode-triode, the potential of saidsupply lying at say 20 volts. The point of connection between the tworesistances R4 and R2 arranged in series is connected through the tworesistances R1 and R3 also arranged in series with the control grid ofthe triode T3 and the mixer grid of the hexode H. There may be inserted,if required, in the connection between fthe two grids a resistance R5.The connecting point between the two resistances Rl. and R3 is grounded-through the condenser C1. The wire feeding triode grid is connectedthrough a condenser `C2. with the yanode -of the hexode.

No sound is produced when the switches K1 to K5 -lie in the openposition as illustrated in the drawing. The negative grid bias of m2Ovolts is transferred through the resistances R2, R1 and R3 to thecontrol grid of the triode T3 and to the mixer grid of the hexode H andas a consequence of this high negative bias, the two tubes are blockedagainst the passage of oscillatory current.

Now if the switch K1 lis closed, its movable contact blade 'connects thewire L with ground. The current, fed by the grid bias supply G to theground through the resistances R2 and R4, produces at the connectionbetween the two last mentioned resistances a potential that is dierentfrom Athat previously prevailing at said point and in fact it assumes nolonger a high Vnegative value. This potential, the Vvalue of which isdefined by the resistances R2 andR4 and that is fed through theresistances Ri and R3 to the control grid of the triode T3 and of themixer grid of the heXode H, is therefore substantially lower than -20volts in absolute value and, in fact, the grid bias is'now of a valuewhich perm'its of passage of oscillatory current through the two tubesand the note defined by the resistance R may develop.

The same procedure is true in case of the closing of any of the otherswitches K2 to K5 or of the Vfurther switches that'are not illustrated.

The value of the grid bias defined by the value given to the resistancesis however not applied to the grids in perfect synchronism with theclosing of any of the switches K, such as the switch Kl; as a matter offact, the condenser 'Cl is already loaded by the negative voltage of thegrid bias supply and it keeps at iirst this high negative potentialstill applied for a short time to the two grids. It discharges thengradually across the resistances Ri and R4 into the wire L and towardsground. It is only when this `discharge is at an end that the value ofgrid potential corresponds tothe desired operativeness. lt is thereforeapparent that the operative potential of the grid is deiined chiefly bythe value of the resistances R2 and R4 andalso of course by the value ofthe resistances R1 and R3 while the time of discharge of the condenserCi depends on its own capacity and on the magnitude of the resistancesR1 and R4. Similarly, the capacity of the condenser C2 .connecting thewire feeding the grids of the combined tubes with the anode of thehexode has action on the length of the transient period. lt should beremarkedthat this condenser may be adjustable so as to provide forthehigher range of notes about one quarter Vof the capacity of thecondenser C2i. Y When the switch Ki. is opened, the opposite successionof steps is provided; the short-'circuitingofthe condenser Cl'across'the resistances Ri and'Ri is first switched @if at Kl. Consequently, thecondenser 'C1 is loaded again through the 'resistances R2 and Rl and it`shifts through the resistance R3 the grid bias back into its blockingvalue.

In order to 'act selectively on the duration ofthe intermediate stagesduring which the grid bias is modiiied, it is possible to adjust thecondenser'C.. This'possibility is illustrated in the drawing by showingthe condenser constituted by aplurality of separate condensers insertedin parallel andthe connection with each of which may -be opened andclosed through corresponding switches.

Throughaction on these switches and through -a selective combination ofthe different condensers, for instance by means of a continuous control,there are provided various possibilities of adjustment, the number ofwhich may be as high as desired.

As illustrated by the wiring diagram, the resistance R1 and thecondenser C2 act on the grid of the triode T3 and also on a grid of thehexode H, the phases of said grids being shifted by 180. By reason ofthis phaseshifting between the two elementary tubes and of the direct orindirect interconnection between the two grids, there is provided acounter-coupling which makes up completely for the undesirableparasitical noises appearing otherwise at the beginning and end of theproduction of a note. It is also an advantage with a view to cutting outany creaking noises that the current owing through the switches isextremelly weak and consequently this allows using for such currentsvery small contact areas in the said switches. The cuts out also theburning of the contact-pieces which leads to a longer life for the musicinstruments without any risk of any disturbances arising.

The frequency generator A received its anode voltage from the supply ofanode voltage A2 while the preliminary amplier B is fed by another anodevoltage supply A1. It is essential for these supplies of anode voltageto be quite independent of each other so that the two sections A and Bmay be quite distinct. It is possible, in fact, to use completelyseparate supplies of anode voltages, but it is also possible to resortto a common supply, as obviously apparent from comparison with theinstruments fed from the mains, the two voltages A1 and A2 oeingstabilized independently of each other, for instance throughcorresponding neon tubes NA and NB so that these voltages may beadjusted permanently to the values required for the two sections A andB. The insertion of these two neon tubes for stabilizing independentlyof each other the voltages A1 and A2 cuts out any action of thefrequency generator A on the preliminary amplifier B and reversely, thisbeing extremely important for the obtention of a perfect reproduction ofmusic.

The amplified oscillatory voltages appearing at the anode of the triodeT3 are iinally fed through the output transformer C and the wire S fedby the latter to the associated tone and volume control and thence tothe amplifier and to the loud speaker.

While I have disclosed several embodiments of the present invention, itis to be understood that these embodiments are given by example only andnot in a limiting sense, the scope of the present invention beingdetermined by the objects and the claims.

I claim:

l. l'n an electronically-operated music instrument, the combination ofmeans for generating audio current pulses with an amplifier connectedwith said pulse generating means and comprising a hexode-triodeincluding a control grid and a mixer grid for the hexode, an anode forsaid hexode, a control grid for said triode and a condenser, the saidmixer grid ot said hexode being connecting to the control grid of saidtriode, and, thereby, over the said condenser to the anode of thehexode, means for blocking the passage of said audio current pulses tosaid control grid of the hexode, a grid bias supply feeding the controlgrid of said triode and the mixer grid of said hexode, and means wherebythe said audio current pulses gradually modify grid bias fed by the saidgrid bias supply in order to arrive at a value allowing operation of thehexode-triode a short time after the initiation of each of said pulsesand gradually returning said bias to its original blocking value at theend of the pulse.

2. The instrument, as set forth in claim l, which the said mixer grid ofsaid hexode is connected directly to the control grid of said triode.

3. The instrument, as set forth in claim l, in which the `said mixergrid is connected to the control grid of said triode by means of aresistance.

4. In an electronically-operated music instrument, the

increasing development of said combination of means for generating audiocurrent pulses' with an amplifier connected with said pulse generatingmeans and comprising a hexode-triode including a control grid and amixer grid for the hexode, an anode for said hexode, a control grid forsaid triode and a condenser, said mixer grid of said hexode beingconnected to the control grid of said triode, and, thereby, over thesaid condenser to the anode of said hexode, means for blocking thepassage of said audio current pulses to the control grid of said hexode,a grid bias supply feeding the control grid of said triode and the mixergrid of said hexode, a network including a capacity and resistancesinserted between said grid bias supply and the control grid of thetriode and the mixer grid of the hexode and means whereby the saidincoming audio current pulses provide a drop in the voltage fed by gridbias supply and the discharge of the network condenser across thenetwork resistance to produce a gradual modification in the grid biasand, thereby, a gradually increasing development of the audio pulsesthrough the hexode-triode and conversely the end of a note produces areloading of said network condenser and returns the grid bias to itsnormal value to produce a gradual throttling of the audio pulses passingthrough the hexode-triode.

5. In an electronically-operated music instrument, the combination ofmeans for generating audio current pulses with an amplifier connectedwith said pulse generating means and comprising a hexode-triodeincluding a control grid and a mixer grid for the hexode, an anode forsaid hexode, a control grid for said triode, and a condenser, the saidmixer grid of said hexode being connected to the control grid of saidtriode, and, thereby, over the said condenser to the anode of. saidhexode, means for blocking the passage of said audio current pulses tothe control grid of said hexode, a grid bias supply feeding the controlgrid of said triode and the mixer grid of said hexode, a networkincluding a capacity and resistances inserted between said grid biassupply and the control grid of said triode and the mixer grid of saidhexode and mounted in parallel with the first condenser, at least one ofwhich capacity and resistance elements is adjustable, and means wherebythe said incoming audio current pulses provide a drop in the voltage fedby the grid bias supply and the discharge of the network condenseracross the network resistance to produce a gradual modification Iin thegrid bias and thereby, a gradually increasing development of said audiopulses through the said hexode-triode and conversely the end of a. pulseproduces a reloading of said network condenser and returns the grid biasto its normal value to produce a gradual throttling of said audio pulsespassing through said hexode-triode.

6. In an electronically-operated music instrument, the combination ofmeans for generating audio current pulses with an amplifier connectedwith said pulse generating means and comprising a hexode-triodeincluding a control grid and a mixer grid for the hexode, an anode forsaid hexode, a control grid for said triode and a condenser, the saidmixer grid of said hexode being connected to the control grid of saidtriode, and, thereby, over the said condenser to the anode of saidhexode, means for blocking the passage of said audio current pulses tothe said control grid of said hexode, a grid bias supply feeding thecontrol grid of said triode and the mixer grid of said hexode, a networkincluding a capacity and resistances inserted between said grid biassupply and the control grid of said triode and the mixer grid of saidhexode and mounted in parallel with the iirst condenser, at least one ofwhich capacity and resistance elements is adjustable, and means wherebysaid incoming audio current pulses provide a drop in the voltage fed bysaid grid bias supply and the discharge of the network condenser acrossthe network resistance to produce a gradual modification in said gridbias and, thereby, a gradually audio pulses through said ansehen" A Yhexode-triode and conversely the end of a ,pulse produces a reloading ofsaid network 'condenser and returns said grid bias to its normal valueto produce a gradual throttling of said audio pulses passing throughsaid hexode-triode and means for coupling the adjustable element of thenetwork with said pulse generating means in a manner such that thedurations of development yof said laudio currents through thehexode-triode and of fthe throttling thereof are smaller for highfrequencies than for low frequencies. i

7. ln an electronically-operated music instrument, thc combination ofmeans for gene 'ng audio current pulses with an amplifier connected withsaid pulse ,generating means and comprising a hexodetriode including acontrol grid and a mixer grid for the hexode, an anode for said hexode,a control grid for said triode and a con- '.enser, the said mixer gridof said hexode being connected to the control grid of said triode, andthereby, over the said condenser to `the anode of said hexodc, means forblocking the passage or said audio current pulses to the control grid ofsaid hexode, a grid bias supply feeding the control grid of said triodeand the mixer grid of said hexode, a network including a capacity andresistances inserted between said grid bias supply and the control gridof said triode and the mixer grid of said hexode and mounted in parallelwith the first condenser, at least one of which capacity and resistanceelements is adjustable, and means whereby said incoming audio currentpulses provide a drop in the voltage fed by said grid bias supply andthe discharge of the network condenser across the network resistance toproduce a gradual modification in said grid bias and thereby, agradually increasing development of said audio pulses passing throughsaid hexode-triode and conversely the end of a pulse produces areloading of said network condenser and returnssaid grid bias to itsnormal value to produce a gradual throttling of said audio pulsespassing through said Vhexode-triode, means for coupling the adjustableelement of the network with said pulse feeding means in a manner suchthat the durations of development of said audio currents through saidhexode-triode and of the throttling thereof are smaller for highfrequencies than for low frequencies and an octave transposition switchcoupled with the adjustable element of the network.

8. in an electronically-operated music instrument, the combination ofmeans for generating audio current pulses with an amplifier connectedwith said pulse generating means comprising a hexode-triode including acontrol grid and a mixer grid for the hexode, an anode for said hexode,a control grid for the triode and a condenser, the said mixer grid ofsaid hexode being connectcd to the control grid of said triode, and,thereby, over the said condenser to the anode of said hexode, forblocking the passage of said audio current pulses to said control gridof said hexode, a Vgrid bias supply feeding the control grid of saidtriode and the mixer grid of said hexode, a first resistance insertedbetween the control grid of said triode and the mixer grid of saidhexode and said grid bias supply, a plurality of switches controllingthe feeding of said pulses corresponding to different notes, a secondresistance disposed in series with the said first resistance and adaptedto be grounded upon operation of any switch and a third resistanceinserted between the point connecting the said first and secondresistances and the hexode-triode grids and including a tapping, and acondenser grounding said tapping.

9. ln an electronically-operated music instrument, the combination ofmeans for generating audio current pulses with an amplifier connectedwith said pulsev generating means and comprising a hexode-triode,including a control grid and `a mixer grid for the-hexode, an anode forsaid hexode, a `control grid forvsaid ytriode and a-'condenser, the saidmixer grid of said nexode being connected to theV control grid of saidtriode, and, thereby, over the said condenser to the anode of saidhexode, means for blocking the passage of said audio current pulses tothe control grid of said hexode,-a grid 'bias supply feeding the controlgrid of said triode and the mixer grid of said hexode, ya firstresistance inserted between the control grid of said triode and themixer grid of said hexode and said grid bias supply, a plurality `ofswitches controlling the feeding of such pulses corresponding todifferent notes, a second resistance mounted in series with the said rstresistance and adapted to be grounded upon operation of'any of saidswitches, and a third resistance inserted between vthe point connectingthe said first and second resistances and said heXode-triode grids andin cluding a tapping, a condenser grounding said tapping, and means forladjusting the said last mentioned condenser to modify the duration ofthe variation .in bias of said hexode-triode grids under the action ofthe grounding of the said second resistance.

l0. ln an electronically-operated music instrument, the combinationofmeans for generating audio current pulses with an amplifier connectedwith said pulse generating means and comprising a hexode-triodeincluding a control grid and a mixer grid for the hexode, an anode forsaid hexode, a control grid for said triode and a condenser, the saidmixer grid of said hexode being con nected to the control grid of saidtriode, and, thereby, over the said condenser to the anode of saidhexode, means for blocking the passage of said audio current pulses tothe control grid of said hexode, a grid bias supply feeding the controlgrid of said triode and the mixer grid of said hexode, means lforadjusting the capacity of said condenser, a first resistance insertedbetween the control grid of said triode and the mixer grid of saidhcxode and said grid 'bias supply, a plurality of switches controllingthe feeding of said pulses cor-responding to different notes, a secondresistance mounted in series with the said first resistance and adaptedto be grounded upon operation of any of said switches and a thirdresistance inserted between the point connecting the said first andsecond resistances and said hexode-triode grids and including a tapping,a condenser grounding said tapping, and means for adjusting the saidlast mentioned condenser to modify the duration of the variation in biasof said hexode-triode grids under the action of the said secondresistance.

1l. In an electronically-operated music instrument, the combination of ahexode-triode including a control grid and a mixer grid for the hexode,an anode for said hexode, a control grid for said triode and acondenser, the said mixer grid of said hexode being connected to thecontrol grid of said triode, and, thereby, over the said condenser tothe anode of said hexode, means for blocking the passage of audiocurrent pulses to the control grid of said hexode, a grid bias supplyfeeding the control grid of said triode and the mixer grid of saidhexode, a double triode frequency generator comprising a first triodeand a second triode feeding the control grid in the hexode with audioicurrent pulses corresponding to different notes, each triode includinga cathode, a control grid and an anode, a grounded potentiometerprovided with an vadjustable tapping, a resistance connecting saidtapping with the anode of said first triode and the grid of said secondtriode, a source of anode supply feeding the anode of the second triodeand connected with the non-grounded end `of said potentiometer', anadjustable resistance inserted between said anode voltage supply andsaid anode of the said seco-nd triode and an adjustable resistancegrounding the cathode of the said first triode and means whereby thesaid laudio current pulses gradually modify grid bias fed by the gridbias supply in order to arrive at a value allowing operation of thehexode-triode a short time vafter the initiation of each of said pulsesand gradually returning saidbias `to its original blocking value at theend of the pulse.

l2. In an electronicallypperated music instrument, the combination of ahexode-triode including a control grid and a mixer grid for the hexode,an anode for said hexode, a control grid for said triode and acondenser, the said mixer grid of said hexode being connected to thecontrol grid yof said triode, and, thereby, over the said condenser tothe anode of said hexode, means yfor blocking the passage of audiocurrent pulses to the control grid of said hexode, a grid bias supplyfeeding the control grid of said triode Iand the mixer grid of saidhexode, -a double triode frequency generator comprising a first triodeand a second triode feeding the control grid of said hexode with audiocurrent pulses corresponding to different notes, each triode including acathode, `a control grid and an anode, an adjustable condenser groundingthe grid of said first triode, a grounded potentiometer provided with anadjustable tapping, a resistance connecting said tapping with the anodeof said first triode and the grid of said second triode, a source ofanode supply feeding the anode of the second triode and connected withthe non-grounded end of said potentiometer, an adjustable resistanceinserted between said anode voltage supply and said anode of the saidsecond triode and an adjustable resistance grounding the cathode lof thesaid first triode and means whereby the said audio current pulsesgradually modify grid bias fed by the grid bias supply in order toarrive at a value allowing operation of said hexode-triode a short timeafter the initiation of each of said pulses and gradually returning saidbias to its original blocking value at `the end of the pulse.

13. In `an electronically-operated music instrument, the combination ofa hexode-triode including a control grid and a mixer grid for thehexode, an anode for said hexode, a control grid for said triode and Iacondenser, the said mixer grid of said hexode `being connected to the`control grid of said triode, and, thereby, over the said condenser tothe anode of said hexode, means for blocking the passage of audiocurrent pulses to the control grid of said hexode, a grid bias supplyfeeding the control grid of said triode and the mixer grid of saidhexode, an anode voltage supp-ly for the anode of said hexode-triode, adouble triode frequency generator comprising `a first triode and asecond triode feeding the control grid in said hexode with audio currentpulses corresponding to different notes, each triode including acathode, a control grid and an anode, a grounded potentiometer providedwith an adjustable tapping, a resistance connecting said tapping withthe anode of the said first triode and the grid of Ithe said secondtriode, independent of the hexode-triode anode voltage supply, a sourceof anode supply feeding the anode of the said second triode andconnected with the non-grounded end Iof said potentiometer, anadjustable resistance inserted between said anode voltage supply andsaid anode of the second triode and an adjustable resistance groundingthe cathode of the said first triode and means whereby the said audiocurrent pulses gradually modify the grid bias fed by the grid biassupply in order to arrive at a value allowing operation `of thehexode-triode a short time after the initiation of each of said pulsesand gradually returning said bias to its original blocking value at theend of the pulse.

14. In an electronically-operated music instrument, the combination of ahexode-triode including a control grid and a mixer grid for the hexode,an anode for said hexode, a control grid for said triode and acondenser, the said mixer grid of said hexode being connected to thecontrol grid of said triode, and, thereby, over the said condenser tothe anode of said hexode, means for blocking the passage of audiocurrent pulses to the control grid of said hexode, a grid bias supplyfeeding the control grid of said triode and the mixer grid of saidhexode, an anode voltage supply for the anode of said hexode-triode, adouble triode frequency generator comprising a first triode and a secondtriode feeding the control grid in said hexode with audio current pulsescorresponding to different notesa each triode including a cathode, acontrol grid and an anode, a grounded potentiometer provided with anadjustable tapping, a resistance connecting said tapping with the anodeof the said first triode and the grid of the said second triode, asource of anode voltage supply feeding the anode of the said secondtriode and connected with the non-grounded end of the potentiometer,separate stabilizers for the voltages fed by the two anode voltagesupplies, an adjustable resistance inserted between the said secondanode voltage supply and said anode of the second triode and anadjustable resistance grounding the cathode of said first triode andmeans whereby the said audio current pulses gradually modify the gridbias fed by said grid bias supply in Iorder to arrive at a valueallowing operation of said hexode-triode Ia short time after theinitiation of each of said pulses and gradually returning said bias toits original blocking value at the end of the pulse.

l5. In an electronically-operated music instrument, the combination of ahexode-triode including a control grid and a mixer grid for the hexode,an anode for said hexode, a control grid for said triode and acondenser, the said mixer grid of said hexode being connected to thecontrol grid of said triode, and, thereby, over the said condenser tothe anode of said hexode, means for blocking the passage of audiocurrent pulses to the control grid of said hexode, a grid bias supplyfeeding the control grid of said triode and the mixer grid of saidhexode, a double triode frequency generator comprising a first triodeand a second triode feeding the control grid in said hexode with audiocurrent pulses corresponding to different notes, each triode including acathode, a control grid and an anode, a system of resistances adapted tofeed selectively the control grid of the said rst triode, meanscontrolling the selective connection of said resistances with thecontrol grid of the said first triode to produce the different desirednotes, a grounded potentiometer provided with an adjustable tapping, aresistance connecting said tapping with the anode of the said firsttriode and the grid of the said second triode, a source of anode supplyfeeding the anode of the said second triode and connected with thenon-grounded end of said potentiometer, `a first resistance insertedbetween said hexode-triode grids and said bias supply with the saidcondenser, a plurality of switches controlling the means controlling theselective connection of the resistances feeding the control grid of thesaid second triode, a second resistance mounted in series with thebias-fed first resistance and adapted to be grounded upon operation ofany of said switches and a third resistance inserted between the pointconnecting said two last mentioned resistances and said hexode-triodegrids and including a tapping, and a further condenser grounding saidtapping.

References Cited in the file of this patent UNITED STATES PATENTS2,245,354 Morz June 10, 1941 2,270,023 Ramsen et al. Ian. 13, 19422,539,826 George Jan. 30, 1951 2,639,639 Schmidt May 26, 1953 OTHERREFERENCES Electronic Engineering, December 1942, pp. 284, 285, A SimpleElectronic Switch, Russell.

